The following is only a recommendation and not explicit instructions. How you choose to do surface preparation is purely your decision.
Proper surface prep is essential. Before applying your new sticker, be certain the surface is smooth, dry and free of any dirt, dust, grease etc. that might hinder it from adhering well. To prepare a surface, thoroughly clean it with a mild soap and water solution or glass cleaner and, for optimal adhesion, follow up with a final wipe using rubbing alcohol to remove any remaining residue. Doing this will help ensure the surface is completely dry and free of contaminants and promote a strong bond between the sticker and surface.